MintyBoost XL: Almost Finished!

Well, I finally drilled my PCB for my MintyBoost XL last night, and it was a great success. If you need PCB drill bits, order them from stevie66 on ebay. I got various sizes from 50 to 85, but I found the 65 to be the most useful. I used it to drill all but the largest holes on the board.
Once that was done, I soldered it all together. It came out very nicely. I struggled the most with the mint tin!
I hooked it up and tested the input: about 2.3v. Then, I carefully tested the USB output power pins: 5.03V! This thing works beautifully.
I found an issue with my implementation of this project, though. The LT1303 IC doesn’t support current above 200mA, so my phone rejects the charge after about 5 seconds. I found out you can request samples directly from Linear, so I’ll be trying out a 1302, and perhaps redesigning the board to use a newer generation chip I’m sampling from Linear Technology.

Overall, this is great for the intermediate electronics nerd who wants to take a circuit from board layout in Eagle to working semi-professional product! I had a lot of fun doing it, and making small modifications will be even more fun.

One thought on “MintyBoost XL: Almost Finished!

  1. ScottInNH

    If you redesign the layout, I’d suggest adding an on-off switch because the LT1302 does have a quiescent current draw that will drain your batteries.

    Natalie from Linear was so helpful to point the current drain out to me when I requested 1302 samples, confirming my suspicions (as my Sanyo Eneloop batteries were not staying as freshly charged as they should have been). Now I just remove the battery (you’re ahead of me… I haven’t tried designing my own boards yet).

    Note that the Adafruit pages say “no on/off switch is necessary”, but they’re either assuming you will not “store” fresh cells in the Minty, or they’re referring to the original Minty v1 which is based on the MAX756 chip. I can’t say which, but with the LT1302 this statement is no longer true.

    Other improvements I considered (which I’ll never get to) would be

    1) switching to surface mount inductor. While surface mount can be a pain, you have many more choices for inductors and they are much cheaper as well. Actually, a much smaller board (under a square inch) would make for a good first order from DorkbotPDX.

    2) A switch for selecting between resistor sets and therefore USB charging modes. The Voltaic website has an even better writeup than Adafruit; Voltaic explain how you can use resistors to get the iPad to charge [screen off] in slower 500ma USB mode. Note the LT1302 can handle 500ma, but the contribution a pair of AA cells could offer makes it a questionable test (but D cells seem more reasonable).

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